Numerical modeling of the churning power losses of gears: an innovative 3D computational tool suitable for planetary gearbox simulation

Thanks to the recent developments in the computer science, simulations are becoming an increasingly widespread approach that can help the designers in the development of new products. In the specific field of gearboxes, simulations up to now have been used mainly for structural and dynamic analysis. In these fields, the simulation tools have proved to be able to provide reliable information. Moreover, in the field of structural design and strength analysis, with respect to the various failure mechanisms involved, many analytical methods and international standard are available. On the other hand, at present for the prediction of the power losses and the efficiency of gears, neither accurate analytical methods nor automated simulation tools are available, in particular where the interest is focused on load independent power losses. The authors have been working on this topic for several years and have developed new methodologies based on computational fluid dynamics. With respect to general-purpose commercial software, the techniques that have been developed by the authors for the specific application of gears and gearboxes, allow a significant reduction of the computational effort and have the capability to take into account particular physical phenomena that occurs in gears, such as cavitation for instance, and for which no information available in literature, concerning their influence on gears efficiency. The purpose of this paper is to introduce an improved automated strategy, implemented in order to extend the applicability of the previously developed computational method to real complex gearboxes. With this additional improvement, some geometrical limitations adopted in the past can be removed and the tool is now suitable for the application to real complex gearboxes. In order to show the capabilities of this new strategy, a planetary gearbox, which represents one of the most complicated kinematic arrangements of gears has been selected and simulated. At the same time, the planetary gearboxes represents a configuration for which the numerical fluid dynamics simulation can give the major contribution tb the calculation of load independent power losses, due to the peculiar interaction between the lubricant and the planets which are supported by a rotating planet carrier. The simulations have been performed both with planar simplified models and with complete 3D models and compared with experimental data showing the goodness of the approach.